A transition to new will start by 2014, enterprise processors based on the "Haswell" microarchitecture will drive the change, according to a VR-Zone report. While client processors based on the Haswell architecture will retain current DDR3 memory standard with a possibility of higher DDR3 clock speeds, enterprise processors under the "Haswell-EX" family will feature the industry's first DDR4 memory controllers for x86. Following that, DDR4 will filter down to future client platforms. Pictured below, is a DDR4 UDIMM by Samsung.

Sources say that, while the mainstream Haswell 4-core platform will still stay on DDR3 - and nothing wrong with that, since by then DDR3 will approach 3000 speed grade - the high end Haswell-EX 4-socket plaform, with each chip having 16 or so cores, will for the first time, support DDR4 memory, in 2014. These monstrous chips, allowing upwards of 60 cores on each four socket mainboard, will bring a new meaning to a 'multi-core monster'. On the memory side, since DDR4 brings lower power consumption with 1.2v power supply, as well as better parity protection and recovery from errors, the benefits are there, even without the speed increase.
 
For the desktop side, the 22 nm Haswell and its 14 nm Broadwell successor would share the same LGA1150 socket, therefore both supporting DDR3 memory only, with DDR4 support likely only with their 2015 successors and a new microarchitecture at that time. So, here we have a one-year lag between high end and the low end for the new generation memory support, with the low end being the late one this time.